The present invention relates to an equalizing and compensating coupling for transfer of large torques, and more particularly the invention relates to a coupling interposed between the output shaft of a transmission gear and the propellor shaft of a ship.
Couplings used for transmission of large torques, particularly in ships drive systems, may have primary and secondary parts which have coaxial disposition to each other and to the respective axis of the couplings, and the two parts are interconnected by rubber-elastic elements. In a particular construction, a coupler sleeve may be interposed, and the primary and secondary clutch parts each connect to the sleeve through these resilient elements.
It is, however, necessary to consider the operating conditions for such a clutch or coupling in some detail. If the transmission of the ships drive is located near the stern, the propeller shaft will be rather short and exhibit rather high flexural stiffness and bending strength. On the other hand the higher strength of sheet metal as it is used for construction of ships hulls today permits employment of thinner sheet stock for that purpose so that the hulls are more resilient. Such increase in resiliency is particularly noticeable in the stern because the buyoncy differs for different loads. The resulting change in shape of the hull must not influence the position of the ship's drive generally and must not cause any change in gearing operation.
Ships gears are quite heavy, and for this reason they cannot merely be connected to the respective propeller shaft. Rather, the transmission must be mounted in some fashion to the frame of the ship. If, however, the propellor shaft moves with flexing of the hull, displacement of gear parts must be expected and has, in fact, been observed.
Several different solutions have been advanced to solve that problem. In accordance with a first solution, a thrust bearing is directly connected to the transmission gear; the latter has a small base bolted to the base of the thrust bearing. The base of the thrust bearing has usually significant strength.
In accordance with a second solution to the problem thrust bearing and transmission are separated, and the transmission is solely responsible for radially guiding the propellor shaft. Any vertical displacements of the bases of the thrust bearing and of the transmission gear is to be compensated in that manner.
In accordance with a third solution the transmission is mounted on level controlled cylinders so that changes in the location of its base are not transmitted to the transmission. Finally, it has been proposed to provide a transversely displaceable jaw clutch between propeller shaft and gearing, which clutch does not only transfer torque but compensates also for disposition changes as between thrust bearing and gearing.
All of these proposals for solving the problem have one drawback or another and are, therefore, not quite suitable, at least not to the desired extent.
A small base in accordance with the first proposal leads invariably to overhanging parts, particularly in twin gear systems. Moreover, a small base is not well suited to take up the reaction forces if the power transmitted is quite large. The separation of transmission and thrust bearing in accordance with the second proposed solution may suffice in the case of vertical, mutual displacement, but not when the angle between propeller shaft and transmission output shaft tends to change.
The levelled positioning of the transmission casing, also known as active positioning, is very complicated and too amenable to break down. The final solution was found to cause increasing stiffening of the jaw clutch with increasing torque while for low torques the clutch my start to rattle.